PRINCIPLE

. . Refraction of a plane wave We will now use Huygens principle to derive the laws of refraction. Let PP represent the surface separating medium and medium , as shown in Fig.

. . Let v1 and v2 represent the speed of light in medium and medium , respectively. We assume a plane wavefront AB propagating in the direction A A incident on the interface at an angle i as shown in the figure.

Let * be the time taken by the wavefront to travel the distance BC. Thus, BC = v1 * In order to determine the shape of the refracted wavefront, we draw a sphere of radius v2* from the point A in the second medium (the speed of the wave in the second medium is v2). Let CE represent a tangent plane drawn from the point C on to the sphere. Then, AE = v2 *and CE would represent the refracted wavefront.

If we now consider the triangles ABC and AEC, we readily obtain sin i =